8 PRESIDENT’S ADDRESS. 
reduced and published! they give an almost exact accordance with the 
value of the solar parallax derived from the heliometer observations of 
the minor planets, Iris, Victoria, and Sappho in 1888 and 1889. 
But in 1931 Eros will approach the Earth within one-sixth part of 
the Sun’s mean distance, and the fau]t will rest with astronomers of that 
day if they do not succeed in determining the solar parallax within one 
ten-thousandth part of its amount. 
To some of us who struggled so hard to arrive at a tenth part of 
this accuracy under the less favourable geometrical conditions that were 
available before the discovery of Eros, how enviable seems the oppor- 
tunity ! 
And yet, if we come to think of it rightly, the true opportunity and 
the chief responsibility is ours, for now and not twenty years hence is the 
time to begin our preparation ; now is the time to study the origin of 
those systematic errors which undoubtedly attach to some of our photo- 
graphic processes ; and then we ought to construct telescopes specially 
designed for the work. These telescopes should be applied to the charting 
of the stars near the path which Eros will describe at its opposition in 
1931, and the resulting star-co-ordinates derived from the plates 
photographed by the different telescopes should be rigorously inter- 
compared. Then, if all the telescopes give identical results for the 
star-places, we can be certain that they will record without systematic 
error the position of Eros. If they do not give identical results, the 
source of the errors must be traced. 
The planet will describe such a long path in the sky during the 
opposition of 1931 that it is already time to begin the meridian observa- 
tions which are necessary to determine the places of the stars that are to 
be used for determining the constants of the plates. It is desirable, 
therefore, that some agreement should be come to with respect to selection 
of these reference-stars, in order that all the principal meridian observa- 
tories in the world may take part in observing them. 
I venture to suggest that a Congress of Astronomers should assemble 
in 1908 to consider what steps should be taken with reference to the 
important opposition of Eros in 1931. 
The Stellar Universe. 
And now to pass from consideration of the dimensions of our solar 
system to the study of the stars, or other suns, that surround us. 
To the lay mind it is difficult to convey a due appreciation of the 
value and importance of star-catalogues of precision. As a rule such 
catalogues have nothing whatever to do with discovery in the ordinary 
sense of the word, for the existence of the stars which they contain is 
generally well known beforehand ; and yet such catalogues are, in reality, 
by far the most valuable assets of astronomical research. 
‘ Monthly Notices R.A.S., Hinks, vol. lxiv. p. 725; Christie, vol. Ixvii. p. 382. 
